Coupled Effect of High Temperature and Heating Time on the Residual Strength of Normal and High-Strength Concretes

This paper is part of a present research that leads to estimate the level of concrete degradation properties altered by high temperatures, especially by using the maturity concept. In order to evaluate the coupled effect of high temperature and heating time on the residual strength of concrete, a series of compressive and indirect tensile tests was performed on normal and high strength concretes. The effect of incorporating polypropylene fibers in high strength concretes was also investigated. Cubical concrete specimens were exposed to different target high temperatures (100, 300, 500 and 700 ºC) for 3, 6 and 9 hours and then cooled in air. Compressive and flexural strengths of these concrete samples were compared with each other and with the unheated samples. Experimental results indicate that concrete strength decreases with increasing temperature and heating time. The grade of concrete affects the residual compressive and flexural strength; the decrease in the strength of ordinary concrete is more than that in High Performance Concrete (HPC), the effect being more pronounced as the heating time increases. Polypropylene fibers were found to have a beneficial effect on residual strength of HPC at least at high temperatures over their melting and vaporization

Modeling the Influence of Limestone Filler on Concrete: A Novel Approach for Strength and Cost

The use of limestone fillers as additions in concrete has grown because they present several advantages over ordinary cements. Production of composite cements has caused a necessary shift in the manufacture process used in the cement industry. Now, it is known that the separate grinding and mixing technology is more convenient in order to produce these cements, called market-oriented or tailor-made cements. However, their optimum formulations require the help of methods of experimental design. In this study, the incorporation of limestone fines and their optimal is analyzed in concrete, where Portland cement was replaced by up to 42 %. The fillers were chosen to be of various particle sizes. The resulting concretes are compared for compressive strength, cement consumption and economic viability. The results obtained indicate the advantage of incorporation of limestone fines in the concretes, as for the same compressive strength at 28 days, savings up to 23% in the consumption of cement were achieved, which represents a significant reduction of energy, raw material consumption and costs. The XRD analyses of samples cured up to 28 days showed that this amelioration is due to formation of new hydrated compounds. It is concluded that an addition of finely ground limestone filler up to 18% gives a better strength for the same cement content and reduces the cost of concrete for the same target strength

K-Means Efficient Energy Routing Protocol for Maximizing Vitality of WSNs

The progress of wireless communication and microelectronics create wireless sensor network, which is a very important field of research, The utilization of Wireless Sensor Network is growing and have a diversity applications like Military applications, Agriculture, Health care, Medical monitoring. The main issue of WSN is energy consumption, where prolonged network lifetime, is important necessity. From the solution proposed the Clustering with k-means is a successful technique for achieving these goals. This work is adaptation of one of the most famous protocol in WSN witch is Low Energy Adaptive Clustering Hierarchy (LEACH) in the clustering phase where the choice of number of clusters and their CHs.sing the k-means method and the distance between nodes and residual energy. Clustering k-means given a best partition with cluster separation. This chapter regulated as below, in section two we discussed related work used k-means to improved vitality of WSN. In the next section, we introduce the proposed adaptation protocol. The simulation resultsusing MATLAB have shown that the proposed protocol outperforms LEACH protocol and optimizes the nodes energy and thenetwork lifetime

Optimal criteria of Algerian blended cement using limestone fines/Alžyrietiškas mišrusis cementas su maltu kalkakmeniu

The effect of substitution of Portland cement by limestone up to 40% as well as its fineness on the physico‐mechanical properties of fresh and hardened cement pastes is studied. The binder was prepared by substitution of cement by limestone filler. Fillers were chosen of various particle sizes and with percentages from 5 to 40. Test results revealed that the replacement of Portland cement by the finest filler of limestone slightly decreases the consistency and the setting times (initial and final). The total porosity decreases and accordingly the compressive strength is improved with the content and fines of limestone. Although limestone has a little accelerating effect on the hydration process of Portland cement, but acts only as a filler reducing the porosity due to its compact structure, in which the compressive strength of the hardened cement paste is enhanced. The XRD and DTA analyses of samples cured up to 28 days showed that this amelioration is due to formation of new hydrated compounds. It is concluded that an addition of finely ground limestone filler only up to 15% gives a better strength. Santrauka Tirtos šviežios ir sukietėjusios cementinės tešlos, kurioje iki 40 % cemento pakeista įvairaus smulkumo maltu kalkakmeniu, savybės. Rišiklis buvo paruoštas dalį cemento pakeitus maltu kalkakmenio užpildu. Užpildo dalelės buvo įvairaus dydžio, o jų kiekis buvo keičiamas nuo 5 % iki 40 %. Tyrimai parodė, kad priedas leidžia sumažinti vandens kiekį, reikalingą tos pačios konsistencijos mišiniui gauti, taip pat cemento rišimosi pradžiai ir pabaigai paankstinti. Sumažėja cementinio akmens suminis poringumas ir atitinkamai padidėja stipris gniuždant cementinio akmens, kuriame yra kalkakmenio priedų. Nors kalkakmenio priedas nedaug pagreitina portlandcemenčio hidratacijos procesą, tačiau veikia kaip užpildas, sutankinantis struktūrą, dėl to labai padidėja sukietėjusio cementinio akmens stipris gniuždant. Bandinių, išlaikytų 28 dienas, rentgenostruktūrinė ir diferencinė terminė analizė parodė, kad pagerėjimas yra dėl susidariusių naujadarų. Apibendrinant galima teigti, kad 15 % malto kalkakmenio priedas turi didžiausią įtaką stiprumo rezultatams. First Published Online: 14 Oct 2010 Reikšminiai žodžiai: kalkakmenio užpildai, cemento tešla, smulkumas, stipris gniuždant